A-Damascenone

Fig. 3 General steps for the conversion of carotenoids into flavor compounds (left) and as example A-damascenone 7 formation from neoxanthin (right).

Konig, W. A, P, Evers, R, Krehber, S. Schulz, C. Fehr, and G. Ohloff, 1989. Determination of the absolute con guration of a-damascenone and a-ionone from black tea by enantioselective capillary gas chromatography. 45 7003-7006. 

BoU P, Andersen B (1962) Alkaloidal glycosides from Solanum dulcamara III. Differentiation of geographical strains by means of thin-layer chromatography. Planta Med. 10 421-432 Bolt AJN, Purkis SW, Sadd JS (1983) A damascenone derivative from Nicotiana tabacum. Phytochemistry 22 613-614... 

Of all these, probably P-phenethyl alcohol (2) comes closest to the odor of fresh rose petals however, mixing all these components does not reproduce the total fine character of the natural oil. It has been determined that a number of trace constituents representing less than 1% of the volatiles are critical to the development of the complete rose fragrance (10). These include cis- and trans-i.ose oxide (1), nerol oxide (12), rose furan (13), /)i7n7-menth-l-en-9-al (14), P-ionone (15), P-damascone (16), and P-damascenone (3). 

Of the 400 volatiles detected in the tomato, only 17 have a positive impact on the flavor profile. Two of the most important ones are also key players in the aroma of roses p-ionone and p-damascenone. Another player is methyl salicylate, a compound we previously encountered in oil of wintergreen. Some of the most important flavor elements are present in very small concentrations but can be perceived by us at these extremely small concentrations. 

In addition to the major components mentioned above, rose oil also contains a number of components which, although present in low concentrations, contribute to the characteristic fragrance [725-73 lb]. Among these are /3-damascenone (see p. 68) and rose oxide (see p. 143). 

Ethyl 2-methylbutanoate, 2-methylbutyl acetate and hexyl acetate contribute most to the characteristic aroma of Fuji apples [49]. In Red Delicious apples, ethyl butanoate, ethyl 2-methylbutanoate, propyl 2-methylbutanoate and hexyl acetate contribute to the characteristic aroma as determined by Charm-Analysis and/or AEDA [50, 51]. In a comparative study of 40 apple cultivars, the highest odour potency or Charm value was found for -damascenone [52]. This compound usually occurs in a glycosidically bound form and is present primarily in processed products owing to hydrolysis of the glycoside bond after crushing fruit cells [53]. -Damascenone has a very low odour threshold with a sweet, fruity, perfumery odour and is not typical of apple aroma in gen-... 

Important aroma compounds of black currant berries have been identified mainly by GC-O techniques by Latrasse et al. [119], Mikkelsen and Poll [115] and Varming et al. [7] and those of black currant nectar and juice by Iversen et al. [113]. The most important volatile compounds for black currant berry and juice aroma include esters such as 2-methylbutyl acetate, methyl butanoate, ethyl butanoate and ethyl hexanoate with fruity and sweet notes, nonanal, /I-damascenone and several monoterpenes (a-pinene, 1,8-cineole, linalool, ter-pinen-4-ol and a-terpineol) as well as aliphatic ketones (e.g. l-octen-3-one) and sulfur compounds such as 4-methoxy-2-methyl-butanethiol (Table 7.3, Figs. 7.3, 7.4, 7.6). 4-Methoxy-2-methylbutanethiol has a characteristic catty note and is very important to blackcurrant flavour [119]. 

Figure G1.1.3 FID gas chromatogram of a direct injection of the headspace above concentrated extract of Concord grape essence using OV101 substrate. Note the size of the methyl anthranilate peak and the absence of a convincing peak for p-damascenone.

Figure G1.1.3 shows a chromatogram of the headspace of Concord grape essence prepared by direct injection. At retention index 1320 is the peak caused by methyl anthranilate, one of the strongest odorants characterizing Concord grapes however, (i-damascenone, the second most potent odorant in Concord grapes, elutes at 1360 but is not visible. This is because P-damascenone is lOOOx more potent (i.e., its odor threshold is lOOOx lower than methyl anthranilate). This is typical result for the direct injection of headspace from natural products. Figure Gl.1.4, on the other hand, shows the injection of an extract of Concord grape essence concentrated 500-fold with the fi-damascenone peak large enough for quantitation.

Figured.1.4 An FID chromatogram of concentrated extract of the same Concord grape essence shown Figure G1.1.3, drawn to display the data on a linear retention index scale. By simply comparing the index of a peak with the data listed in the flavornet, the odorants that have similar retention indices can be determined. Notice how large the methyl anthranilate peak is, but still no convincing peak for p-damascenone, even though both compounds have the same odor activity (intensity).

Safeguards. All materials will be tested at levels no higher than those found in natural products, e.g., beta-damascenone occurs in apples at 100 times its threshold and will not be used at a level higher than 100 times its average reported threshold. Total intake will be limited to 1 ng per day (less than in an apple) in situations where swallowing is necessary. Rinse water and crackers will be provided to help dissipate any unpleasant residual sensations. Exposure will be limited to six sessions per day. 

In an alcohol-free beer, the concentrations of the beer odorants were 5 to 10-fold lower than in the pale lager beer [18] suggesting that the former beer is a very appropriate matrix for the determination of odor thresholds. A determination of the odor thresholds in the alcohol-free beer revealed (Table 15) that, compared to water, the odor threshold of all odorants increased, but to a different extent. For instance, the threshold of (E)-B-damascenone increased by a factor of 2500, while that of HDF was enhanced only by a factor of eight. Odor activity values calculated on the basis of the odor thresholds in the alcohol-free beer (Table 15) now confirmed the significant contribution of HDF to the dark beer flavor. 

The precursor structures can be elucidated by HRGC/MS and HRGC/FTTR of the acetylated derivatives or aglycons, respectively. Very recently, direct LC/MS measurement of a non-derivatized precursor glycoside of (E)-B-damascenone isolated from apples has been reported [100]. Application of such techniques on precursor fractions from wine [97, 101]... 

Thus the natural product damascenone 10, responsible in part for the smell of roses, cyclises in acid to the cation 11 that can lose a proton from one side only to give3 12. The disconnection for the Nazarov reaction is of the single bond in the five-membered ring opposite the carbonyl group 12a. 

In a more recent study, Bailly et al. (2009) investigated the stability of key odorants during bottle aging in Sautemes wines. Except for 3SH, polyfunctional thiols were found unstable. However, most other key odorants (e.g., sotolon, phenylethanol, esters, y-lactones, p-damascenone, etc.) were still detected within 5-6 years. 

Table 20.1 shows the detection thresholds of a number of perfume materials in air and in water. Note the tremendous range (from 0.002 parts per billion for beta-damascenone to 10,000 parts per billion for phenylacetic acid—both taken in water solutions), the large difference between optical isomers of the same substance (e.g., Nootkatone and alpha-damascone), and the large differences in thresholds reported by different investigators (e.g., benzaldehyde and vanillin). In substances with relatively high water solubility such as vanillin and ethyl vanillin, benzaldehyde, phenylethyl alcohol, and phenylacetic acid, the thresholds in water are very much higher than in air. In poorly water-soluble substances such as pinene and the macrocyclic musk cyclopentadecanolid, the reverse is true. The relative thresholds of a substance in different solvents indicate its performance in different application environments. Substances whose thresholds in water solution are much... 

The significance of a minor component having an important contribution to the odour qualities is illustrated by P-damascenone. Although only present at about 0.14%, it gives 70% of the total odour. 

Fig. 4.6 Mechanisms of formation of a terpenes from geraniol and geranyl glucoside b p-damascenone from megastigm-5en-7yne-3,9-diol and its glucoside...

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